1. Field of the Invention
The present invention relates to a manufacturing method of rigid flexible printed circuit board, more particularly to a manufacturing method of a multi-layer flexible circuit that can be bent to different angles without the need of cutting needless parts and covering the protective barrier on flat cable positioned on the middle of the flexible basefilm.
2. Description of the Prior Art
Single-sided circuits are the mostly broadly used and the simplest circuits. However, the design of electric circuits is getting so complicated that the area of circuit board is too large for practice by single-sided circuit. Accordingly multi-layer circuits are created for replacing single-sided circuits and the circuits are also shaped in multi-planar configurations. The size of circuit board is reduced for the application of complicated circuits.
A lot of electric apparatus such as palm computers, mobile phones etc is folded for saving storage space so that the circuit boards on different shells must be connected with others and able to be folded. The conventional circuit board is a flexible circuited board with rigid outer layer circuit boards on two lateral sides so as to be folded at the flexible portion on the middle part.
The fabricating process of conventional multi-layer circuits is shown in FIG. 8. Inner layer circuit (a1) is made on two lateral sides of both sides of the flexible basefilm (a) which is clad with copper foil on top and bottom sides. And flat cable (a2) for connection is disposed between the two parts of inner layer circuit (a1).
Afterwards, a dielectric bondfilm (b) with reinforced fiber is laminated on the inner layer circuit (a1) on both sides of the flexible basefilm (a) respectively. The dielectric bondfilm (b) is provided with a rectangular hole (b1) so that the flat cable (a2) on the middle of the flexible basefilm (a) is exposed without covering when the dielectric bondfilm (b) is coated on the flexible basefilm (a). Then an outer copper foil (c) with an insulating layer (c1) thereof is stacked on the top of the inner layer circuit (a1). The outer copper foil (c) also has a rectangular hole (c2) with the same function as the previous one (b1). A number of through holes (d) are drilled on connecting points of preset circuit on the outer copper foil (c), as shown in FIG. 9. After being metalized and plated, the plated layer (e) of these through holes is used for electrical conductivity from the outer copper foil (c) to inner layer circuit (a1). Outer layer circuit (a1) is shaped on the outer copper foil (c) and then is covered by solder resist mask (f). At last, the needless sides (g) on two lateral of the dielectric bondfilm (b) and the outer copper foil (c), as shown in FIG. 10, are sectioned and throw away, thus the multi-layer circuits are produced.
During the fabricating process of conventional multi-layer circuits, the dielectric bondfilm (b) must be provided with a rectangular hole (b1) prior to being manicated to other layer, so as the outer copper foil (c). And the the needless sides (g) also need to be cut out. These inconvenience and trouble during the process will increase the manufacturing cost. In addition, the lamination of the dielectric bondfilm (b) and the outer copper foil (c) onto the flexible basefilm (a) must be quite precise that is not easy to achieve during the manufacturing process. The flat cable (a2) on the middle of the flexible basefilm (a) need to be coated with a layer of protective barrier (f1) while the flat cable (a2) and the adjacent outer copper foil (c) are in different layer so that not all surface of the flat cable (a2) can be coated by the protective barrier (f1). Thus the manufacturing process is getting more difficult.
It is therefore a primary object of the present invention to provide a foldable multi-layer circuit board that the outer copper foil with bondfilm on the bottom thereof that doesn""t include reinforced fiber is directly laminated so that the cutout of redundant parts of the laminate and the inconvenience of localization can be avoided.
A further object of the present invention is to provide a foldable multi-layer circuit board that the outer copper foil with bondfilm, which doesn""t include reinforced fiber, on the bottom is directly laminated to the laminate and the outer copper foil on the top of the flat cable is removed at the same time as being made outer layer circuit. Hence it is not necessary to cover a layer of protective barrier on the flat cable on the middle of the flexible basefilm.